1. Field of the Invention
The present invention relates generally to gas turbine engines and, more particularly, to improved leakage control in gas turbine engines.
2. Description of the Prior Art
Conventional gas turbine shroud segments are manufactured as a full ring and later straight-cut into segments to provide joints which allow for thermal growth. The intersegment gap is typically minimized at the highest power settings, when the segments are at their maximum operating temperature and thus greatest length due to thermal expansion. At lower power, the segments do not expand as much and the gaps do not close down and thus seals are typically required. When seals (e.g. feather seals) are not used, these gaps become the prime leak path for shroud cooling air, which is thermodynamically expensive. It is therefore important to minimize the gaps.
As shown in FIG. 1a, the opposed ends of each conventional shroud segment 5 are straight cut to provide parallel mating faces 7 between adjacent segments 5. At room temperature each pair of adjacent shroud segments 5 defines a gap 7. In operation, the shroud segments 5 do not have uniform temperature distribution (the upstream side of the shroud segments 5 is typically exposed to higher temperature than the downstream side thereof). As shown in FIG. 1b, this causes non-uniform thermal expansion and thus non-optimized intersegment gaps in operating conditions. The shroud segments 5 will be hotter upstream and cooler downstream of the gas path, which makes the thermal expansion uneven and creates a larger gap on the downstream side where air can escape the cavity defined about the shroud segments 5. As shown in FIG. 1b, the high thermal expansion will reduce the gap on the upstream side of the shroud segments 5, whereas the low thermal expansion will leave a larger gap on the downstream side of the segments 5.